[20171121]rman backup as copy 2.txt

[20171121]rman backup as copy 2.txt

--//昨天测试backup as copy ,备份时备份文件的文件头什么时候更新.是最后完成后还是顺序写入备份文件.

--//我测试的数据文件使用数据文件2(表空间sysaux),也许是文件不够大,应该减慢备份速度来测试看看.

1.环境:

SCOTT@book> @ &r/ver1

PORT_STRING                    VERSION        BANNER

------------------------------ -------------- --------------------------------------------------------------------------------

x86_64/Linux 2.4.xx            11.2.0.4.0     Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

$ cat dump_head.sh

#! /bin/bash

for i in $(seq 1000)

do

#   echo $i

    xxd -c32 -g 2 -s 8192 -l 32 $1 >> /tmp/dump_head.txt 2>/dev/null

    sleep 1

done

2.测试:

--//首先启动dump_head.sh脚本,session 1:

$ .  dump_head.sh /home/oracle/backup/tea01.dbf &

--//在sesion 2,在rman下执行备份:

RMAN> CONFIGURE CHANNEL 1 DEVICE TYPE DISK RATE 1M;

using target database control file instead of recovery catalog

new RMAN configuration parameters:

CONFIGURE CHANNEL 1 DEVICE TYPE DISK RATE 1 M;

new RMAN configuration parameters are successfully stored

RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;

old RMAN configuration parameters:

CONFIGURE DEVICE TYPE DISK PARALLELISM 3 BACKUP TYPE TO BACKUPSET;

CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;

--//设置DISK RATE 1M,这样可以减慢备份的速度,便于观察.并且仅仅打开1个并行.

RMAN> backup as copy datafile 6 format '/home/oracle/backup/%b';

Starting backup at 2017-11-21 09:43:09

using channel ORA_DISK_1

channel ORA_DISK_1: starting datafile copy

input datafile file number=00006 name=/mnt/ramdisk/book/tea01.dbf

output file name=/home/oracle/backup/tea01.dbf tag=TAG20171121T094309 RECID=17 STAMP=960630229

channel ORA_DISK_1: datafile copy complete, elapsed time: 00:00:45

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

channel ORA_DISK_1: throttle time: 0:00:40

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Finished backup at 2017-11-21 09:43:54

Starting Control File and SPFILE Autobackup at 2017-11-21 09:43:54

piece handle=/u01/app/oracle/fast_recovery_area/BOOK/autobackup/2017_11_21/o1_mf_s_960630234_f1716tsv_.bkp comment=NONE

Finished Control File and SPFILE Autobackup at 2017-11-21 09:43:55

--//注意看下划线内容,throttle time: 0:00:40.

throttle

英 [?θr?tl] 美 [?θrɑ:tl]

n.

节流阀;喉咙，气管;[机]风门

vt.& vi.

扼杀，压制;勒死，使窒息;使节流;（用节汽阀等）调节

vi.

节流，减速;窒息

-----------------------------------------------

--//而我的备份文件就是40M+8k的数据文件.

$ ls -lh /home/oracle/backup/tea01.dbf

-rw-r----- 1 oracle oinstall 41M 2017-11-21 09:43:49 /home/oracle/backup/tea01.dbf

$ ls -l /home/oracle/backup/tea01.dbf

-rw-r----- 1 oracle oinstall 41951232 2017-11-21 09:43:49 /home/oracle/backup/tea01.dbf

--//session 1:

$ fg

. dump_head.sh /home/oracle/backup/tea01.dbf

^C^

3.检查/tmp/dump_head.txt输出记录:

$ uniq -c /tmp/dump_head.txt

      1 0002000: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000  ................................

     40 0002000: 00a2 0000 0100 8001 0000 0000 0000 0105 81a6 0000 0000 0000 0000 0000 0000 0000  ................................

     14 0002000: 0ba2 0000 0100 8001 0000 0000 0000 0104 61c1 0000 0000 0000 0004 200b 6e21 b74f  ................a?....... .n!.O

--//^_^,再次验证我的判断.

--//从以上输出可以发现使用backup as copy备份,一定先建立一个空文件,输出一堆0000(需要大约1秒),大小与数据文件一致,这样可以先检测是否磁盘满足备份需求.

--//然后写入开头00a2,出现40次(我脚本执行sleep 1,不考虑其它消耗正好是40秒).

--//到最后才更新as copy方式的备份映像的文件头.

--//oracle的设计确实考虑许多因素,与备份文件集模式一样最后写入文件头信息,这样保证使用备份image是正确的,

--//设想一下,如果顺序写入备份image文件,如果备份过程中发生中断,而那这个image备份文件来恢复,会发生什么情况呢?

--//而现在这样设计意味着发生中断,备份image的文件头是"坏"的,意味着不能用于恢复.

--//还有一个疑问,写入备份image的文件头信息是 开始备份前读取的文件头信息,然后最后完成备份在读取文件头信息呢?

--//我只要在备份过程发出alter system checkpoint就知道.

--//  重复测试看看.

RMAN> delete datafilecopy all ;

SYS@book> SELECT file#, CHECKPOINT_CHANGE#, CHECKPOINT_TIME,CREATION_CHANGE#  , RESETLOGS_CHANGE#,status, CHECKPOINT_COUNT,fuzzy,name,tablespace_name  FROM v$datafile_header;

FILE# CHECKPOINT_CHANGE# CHECKPOINT_TIME     CREATION_CHANGE# RESETLOGS_CHANGE# STATUS  CHECKPOINT_COUNT FUZ NAME                             TABLESPACE_NAME

----- ------------------ ------------------- ---------------- ----------------- ------- ---------------- --- -------------------------------- ---------------

    1        13279819419 2017-11-21 10:22:57                7            925702 ONLINE              1246 YES /mnt/ramdisk/book/system01.dbf   SYSTEM

    2        13279819419 2017-11-21 10:22:57             1834            925702 ONLINE              1247 YES /mnt/ramdisk/book/sysaux01.dbf   SYSAUX

    3        13279819419 2017-11-21 10:22:57           923328            925702 ONLINE              1156 YES /mnt/ramdisk/book/undotbs01.dbf  UNDOTBS1

    4        13279819419 2017-11-21 10:22:57            16143            925702 ONLINE              1243 YES /mnt/ramdisk/book/users01.dbf    USERS

    5        13279819419 2017-11-21 10:22:57           952916            925702 ONLINE              1152 YES /mnt/ramdisk/book/example01.dbf  EXAMPLE

    6        13279819419 2017-11-21 10:22:57      13276257767            925702 ONLINE               634 YES /mnt/ramdisk/book/tea01.dbf      TEA

6 rows selected.

Starting backup at 2017-11-21 10:26:10

....等

--//session 2:

----- ------------------ ------------------- ---------------- ----------------- ------- ---------------- --- -------------------------------- ----------------

    6        13279819660 2017-11-21 10:26:10      13276257767            925702 ONLINE               635 YES /mnt/ramdisk/book/tea01.dbf      TEA

--//注意看数据文件6的CHECKPOINT_CHANGE#=13279819660(备份开始前CHECKPOINT_CHANGE#=13279819419),说明在备份开始时要做文件检查点, 更新文件头scn.

SYS@book> alter system checkpoint ;

System altered.

--//在备份的过程中我发3次alter system checkpoint ;

output file name=/home/oracle/backup/tea01.dbf tag=TAG20171121T102610 RECID=19 STAMP=960632810

channel ORA_DISK_1: throttle time: 0:00:39

Finished backup at 2017-11-21 10:26:55

Starting Control File and SPFILE Autobackup at 2017-11-21 10:26:55

piece handle=/u01/app/oracle/fast_recovery_area/BOOK/autobackup/2017_11_21/o1_mf_s_960632816_f173qj22_.bkp comment=NONE

Finished Control File and SPFILE Autobackup at 2017-11-21 10:26:57

FILE# CHECKPOINT_CHANGE# CHECKPOINT_TIME     CREATION_CHANGE# RESETLOGS_CHANGE# STATUS  CHECKPOINT_COUNT FUZ NAME                                               TABLESPACE_NAME

----- ------------------ ------------------- ---------------- ----------------- ------- ---------------- --- -------------------------------------------------- ------------------------------

    1        13279819678 2017-11-21 10:26:26                7            925702 ONLINE              1249 YES /mnt/ramdisk/book/system01.dbf                     SYSTEM

    2        13279819678 2017-11-21 10:26:26             1834            925702 ONLINE              1250 YES /mnt/ramdisk/book/sysaux01.dbf                     SYSAUX

    3        13279819678 2017-11-21 10:26:26           923328            925702 ONLINE              1159 YES /mnt/ramdisk/book/undotbs01.dbf                    UNDOTBS1

    4        13279819678 2017-11-21 10:26:26            16143            925702 ONLINE              1246 YES /mnt/ramdisk/book/users01.dbf                      USERS

    5        13279819678 2017-11-21 10:26:26           952916            925702 ONLINE              1155 YES /mnt/ramdisk/book/example01.dbf                    EXAMPLE

    6        13279819678 2017-11-21 10:26:26      13276257767            925702 ONLINE               638 YES /mnt/ramdisk/book/tea01.dbf                        TEA

--//看看备份写入的scn是13279819678还是13279819660呢?

BBED> p /d filename '/home/oracle/backup/tea01.dbf' block 1 kcvfh.kcvfhckp.kcvcpscn

struct kcvcpscn, 8 bytes                    @484

   ub4 kscnbas                              @484      394917772

   ub2 kscnwrp                              @488      3

BBED> p /d filename '/mnt/ramdisk/book/tea01.dbf' block 1 kcvfh.kcvfhckp.kcvcpscn

   ub4 kscnbas                              @484      394917790

SYS@book> select power(2,32)*3+394917772 from dual ;

POWER(2,32)*3+394917772

-----------------------

            13279819660

SYS@book> select power(2,32)*3+394917790 from dual ;

POWER(2,32)*3+394917790

            13279819678

--//从CHECKPOINT_CHANGE#的scn号可以看出是备份文件的文件头信息是备份时读取的文件头信息,而不是经过多次alter system checkpint后的信息.

--//也就是备份时已经读取这部分信息到内存(下面的补充测试也说明问题),最后在写入备份image的文件头的.

--//我再次修改我的测试脚本,-s 8676对应的CHECKPOINT_CHANGE#号信息.再次重复测试,仅仅贴出结果.

    xxd -c32 -g 2 -s 8676 -l 32 $1 >> /tmp/dump_head.txt 2>/dev/null

$ grep "^0002000:" /tmp/dump_head.txt  | uniq -c

     39 0002000: 0ba2 0000 0100 8001 0000 0000 0000 0104 1292 0000 0000 0000 0004 200b 6e21 b74f  .......................... .n!.O

$ grep "^00021e4:" /tmp/dump_head.txt  | uniq -c

     40 00021e4: 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000  ................................

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~    

     77 00021e4: 73fc 8917 0300 0000 f91b 4239 0100 0000 c003 0000 875a 0100 1000 313b 0200 0000  s?.....?B9....?...Z....1;....

--//可以看出前面40秒,根本没有写入文件头scn信息.最后才写入的.

--//收尾还原:

RMAN> configure channel 1 device type disk clear;

old RMAN configuration parameters are successfully deleted

released channel: ORA_DISK_1

RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 3 BACKUP TYPE TO BACKUPSET;